Bus system and apparatus for reducing the reactance of electric furnaces



April 7, 1964 A. PERSSON 3,128,411

A. J. BUS SYSTEM AND ARATUS FOR REDUCING THE REACTANCE ELECTRIC FURNACES Filed NOV. 22. 1960 V 5 Sheets-Sheet 1 v JOHN A ge fi' u 29912.

ATTORNEY J. A. PERSSON BUS SYSTEM AND APPARATUS FOR REDUCING THE REACTANCE OF ELECTRIC FURNACES April 7, 1964 3 Sheets-Sheet 2 Filed Nov. 22, 1960 INVENTOR. JOHN A. PERSSON 742M41 ATTORNEY April 7, 1964 J. A. PERSSON 3,128,411

BUS SYSTEM AND APPARATUS FOR REDUCING THE REACTANCE OF ELECTRIC FURNACES Filed Nov. 22, 1960 3 Sheets-Sheet 3 ATTdRNEr United States Patent 3,128,411 BUS SYSTEM AND APPARATUS FOR REDUCING THE REACTANCE 0F ELECTRIC FURNACES John A. Persson, Buffalo, N.Y., assignor to Union Carbide Corporation, a corporation of New York Fiied Nov. 22, 19st), Ser. No. 70,972 2 Claims. (Cl. 314-31) This invention relates to an improved bus system and apparatus for reducing the reactance in the distribution circuit of three phase electric furnaces.

In general, conventional three phase electric furnaces have the electrodes thereof vertically positioned and ar ranged in a triangular configuration with the electrodes located at the apexes of the triangle. Three phase electrical current is conducted from transformers throng?- interleaved conductors to the vicinity of the furnace structure and from there, through a furnace bus system, including flexible conductors, to the electrodes. The amount of inductance present in the electrical distribution circuit, which includes the interleaved conductors and the furnace bus system, is of great significance in the operation of electric furnaces. The presence of a large amount of inductance in the furnace bus system has serious deleterious consequences, for example, reduced electrical eificiency, reduced power factor and possible electrode circuit instability.

In conducting electrical energy from the transformers to the vicinity of the furnace structure, interleaving of the current carrying conductors provides some reduction of inductive reactance in the distribution circuit. However, the furnace bus systems presently employed in the art for connecting the interleaved conductors to the electrodes do not provide any further substantial reduction in the inductive reactance of the distribution circuit, primarily because the circuits and arrangements of the furnace bus systems of the prior art fail to provide effective flux cancellation between the various conductors employed therein. This failure results in the presence of a substantial inductive reactance in the furnace bus system which causes the furnace operation to be less efiicient, instability prone, and at times incapable of even minimum satisfactory performance.

Accordingly, it is an object of the present invention to provide, in the distribution circuit of a three phase electric furnace, an improved furnace bus system to minimize the inductive reactance in the distribution circuit.

It is another object of this invention to provide, in combination, an improved furnace bus system and an apparatus for supplying current to the electrodes in the furnace whereby the inductive reactant in the distribution circuit of the furnace is minimized.

These and other objects will be apparent from the drawing, specification and claims.

With reference to the drawing:

FIGURE 1 shows a plan View of an improved furnace bus system of the present invention adapted to provide delta excitation for the electrodes of a three phase furnace.

FIGURE 2 shows a modification of the furnace bus system of FIGURE 1. 7

FIGURE 3 is a fragmental elevational view showing an apparatus for supplying current to the electrodes of a three phase electric furnace in combination with the furnace bus system of FIGURE 1.

FIGURE 4 is a sectional plan view of the apparatus of FIGURE 3 taken along 4-4 of FIGURE 3.

FIGURE 5 shows a furnace bus system of the present invention adapted to provide Y excitation for the electrodes of a three phase electric furnace.

In FIGURE 1 electrodes 1, 3 and 5 are shown arranged in a triangular configuration and positioned to extend "ice downward into an electric furnace 7. Transformers 9, 11 and 13 provide separate time displaced phase voltages suitable for the three phase excitation of the electrodes. Conductors 15, 17 and 19, which are usually interlaced in accordance with conventional techniques, connect transformers 9, 11 and 13 to terminals 21, 23 and 25, located on or in the vicinity of the furnace 7.

The furnace bus system of the present invention includes three separate pairs of conductors A, B, and C. The conductors 2'7 and 29 of pair A are arranged in close proximity for the purpose of flux cancellation; for example, they may be arranged closely in parallel. Similarly, conductors 31 and 33 of pair B and conductors 35 and 37 of pair C are arranged in close proximity for flux cancellation. It is seen that the pairs of conductors, A, B and C extend toward the interior of the electrode configuration to different positions substantially within the electrode configuration and closely adjacent to different sides thereof. The conductors 27 and 29 of pair A are separated at a position closely adjacent to the electrode configuration with conductor 27 extending to and connecting with electrode 1 and conductor 29 extending to and connecting with electrode 3. The conductors of pairs B and C are similarly separated and extended to the electrodes for connection therewith, to provide delta excitation for the electrodes. It may be seen in FIGURE 1, by noting the instantaneous direction of current flow illustrated therein, that between terminals 21, 23 and 25 and the respective positions where the conductors of the pairs are separated, flux cancellation is theoretically perfect, thus ensuring a low value of inductive reactance in the furnace excitation system. In addition, the arrangement of FIGURE 1 utilizes the minimum necessary length of conductors thereby providing minimum power loss in the bus system and consequently improved electrical efiiciency.

FIGURE 2 shows a modification of the furnace bus system of FIGURE 1 wherein the conductor pairs A, B, and C, with the respective conductors of each pair, 27 and 2h, 31 and 33, and 35' and 37', arranged in close proximity, extend through different sides of the electrode configuration to positions interior the electrode configuration substantially equidistant from the electrodes. The conductors of the respective pairs are separated at these equidistant positions and extend directly to the various electrodes to provide a delta electrode excitation. In this form of the present invention, not only is flux cancellation theoretically perfect between terminals 21, 23 and 25 and the respective positions where the conductors of the pairs are separated, but in addition, substantial flux cancellation is provided for the separated conductors by arranging the separated conductors which extend to a common electrode in close proximity, as illustrated in FIGURE 2.

In a preferred form, the conductors comprising the furnace bus system are arranged at substantially the same level with respect to the longitudinal axes of the electrodes. This permits the employment of minimum lengths for the conductors of the bus system thereby providing minimum inductance and, in addition, minimum power loss in the bus system. Further, such an arrangement utilizes only a small proportion of the electrode configuration, thus readily permitting advantageous location of furnace equipment, such as gas headers, charge spouts, and the like, in the vicinity of the furnace structure.

In a further embodiment of the present invention an apparatus for supplying current to the electrodes is provided in combination with the furnace bus system of the present invention. This combination is shown in FIG- URE 3 and a plane View along 4-4 of FIGURE 3 is illustrated in FIGURE 4.

With reference to FIGURES 3 and 4, it is seen that electrodes 1, 3 and 5 are respectively provided with electrically conductive cylinders 39, 41 and 43. Each cylinder surrounds a longitudinal portion of an electrode and is spaced therefrom. The cylinders 39, 41 and 43 are located at a common level along the longitudinal axes of the electrodes and are respectively provided with electrically conductive .contacts 45, 47 and 49, and clamps 51, 53 and 55. The clamps serve to maintain the contacts in electrical contacting relation with the electrodes. In FIG- URE 4, the conductors of the bus system 27", 29", 31", 33", 35" and 37" are shown to be arranged generally as in FIGURE 2 and are electrically connected to the cylinders through electrically conductive equalizer rings 57, 59 and 61 and flexible electrically conductive straps indicated as 63. The conductors of the bus system are arranged to be spaced away from contacts 45, 47 and 49 which are most generally located at a relatively short distance from the high temperature regions of the electrodes, i.e. the tips of the electrode (not shown).

In FIGURES 3 and 4, it may be seen that the path of electric current to the electrodes is through equalizer rings 57, 59 and 61, straps 63, and cylinders 39, 41, and 43. The provision of electrically conductive cylinders in place of solid conductors having similar current carrying capacity provides a substantial flux cancellation and hence substantially reduces the reactance of the electrode distribution circuit. In addition, by arranging the conductors of the bus system at a common level with respect to the longitudinal axes of the cylinders, as shown in the drawing, there is no flux linkage, i.e. no inductance between the vertical cylinders and the horizontally disposed conductors of the bus system. By virtue of the fact that the reactance in the electrode distribution circuit is greatly minimized through the use of the above described combination, it is possible to locate the bus system of the combination remote from the high temperature portion of the electrodes while nevertheless ensuring stable and eificient operation of the electrodes. Further, the embodiment of the invention illustrated in FIGURES 3 and 4 may be conveniently enclosed by suitable means to protect the bus system from corrosive attack due to furnace gases, while the use of flexible straps 63 between the equalizer rings and the cylinders permit the electrodes and cylinders to, be adjusted vertically.

Although the furnace bus system of the present invention has been described hereinabove for providing delta excitation for the electrodes, a Y-connected bus system in accordance with the present invention is readily provided as may be seen in the modification of the present invention illustrated in FIGURE 5. In FIGURE 5 three phase electrical energy is conducted from transformers 9, 11 and 13 to terminals 21, 23, and 25 by way of conductors 15, 17 and 19. Three pairs of conductors C, D, and E extend from the terminals, exterior the electrode configuration, to difierent positions substantially within the electrode configuration and closely adjacent to different sides of the configuration where the closely arranged conductors of each pair are separated. Conductors 65, 67 and 69 from pairs C, D and B respectively are joined in a common electrical connection; and the remaining conductors 71, 73 and 75 are connected to different electrodes thereby providing a Y excitation therefor. It is apparent from the current directions indicated in FIG- URE 5 that substantial flux cancellation is provided in the Y-connected bus system of the present invention; and by extending conductors 71, 73 and 75 of pairs C, D and E to positions substantially equidistant from the electrodes, as shown in dotted lines, a further flux cancellation is provided in the Y-connected furnace bus system.

It may be seen from the above description and drawing that a novel bus system and apparatus for the excitation of a three phase electric furnace is provided which represents a beneficial contribution to the art. The present invention, by providing optimum flux cancellation in a furnace bus system ensures reduced reactance in the distribution circuit of the furnace, improved power factor and electrical efiiciency, and improved system stability, thereby making it possible to readily maintain a balanced three phase load in an electric furnace. In the practice of the present invention, the reactance of the furnace excitation circuit is reduced by thirty percent or more in comparison with the furnace bus systems of the prior art.

What is claimed is:

1. An improved bus system for supplying current to a three phase electric furnace having three electrodes arranged in a triangular configuration, said bus system comprising three pairs of conductors, each pair being adapted to be connected exterior the electrode configuration to separate-phase voltages and-each pair having the conductors thereof in close proximity for flux cancellation and extending from exterior the triangular electrode configuration through different sides thereof to different positions interior the electrode configuration substantially equidistant from all the electrodes, the conductors of each pair being separated at said equidistant positions, one separated conductor of each given pair extending directly to one of the electrodes defining the side of the configuration through which said given. pair passes and the other separated conductor of the given pair extending directly to the other electrode defining the side of the configuration through which said given pair passes; the conductors extending to a common electrode being arranged in close proximity for flux cancellation and connected to each other at the common electrode.

2. A bus system and apparatus for supplying current to a three phase electric furnace having three electrodes arranged in a triangular configuration comprising, in combination, three electrically conductive cylinders arranged at a substantially common level along the longitudinal axes of the electrodes each cylinder enclosing a longitudinal portion of a different electrode and spaced therefrom; contact means for connecting each cylinder to the electrode surrounded thereby; three pairs of conductors located at common level parallel to the level of the cylinders and spaced away from said contact means in a direction away from the tips of the electrodes; each said pair of conductors being adapted to be connected exterior the electrode configuration to separate phase voltages and each pair having the conductors thereof arranged in close proximity for flux cancellation and all said pairs extending from exterior the electrode configuration through different sides thereof to diiferent positions interior the electrode configuration substantially equidistant from all the electrodes, the conductors of each pair being separated at said equidistant positions, one separated conductor of each given pair extending directly to the cylinder enclosing one of the electrodes defining the side of the configuration through which said given pair passes and the other separated conductor of the given pair extending directly to the cylinder enclosing the other electrode defining the side of the configuration through which said given pair passes; the conductors extending to a common cylinder being arranged in close proximity for flux cancellation and connected to each other at the common cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 2,368,998 Nissim Feb. 6, 1945 2,853,636 Ploen Sept. 23, 1958 2,908,736 Ernst Oct. 13, 1959 OTHER REFERENCES German application 1,086,423, August 14, 1958. 

2. A BUS SYSTEM AND APPARATUS FOR SUPPLYING CURRENT TO A THREE PHASE ELECTRIC FURNACE HAVING THREE ELECTRODES ARRANGED IN A TRIANGULAR CONFIGURATION COMPRISING, IN COMBINATION, THREE ELECTRICALLY CONDUCTIVE CYLINDERS ARRANGED AT A SUBSTANTIALLY COMMON LEVEL ALONG THE LONGITUDINAL AXES OF THE ELECTRODES EACH CYLINDER ENCLOSING A LONGITUDINAL PORTION OF A DIFFERENT ELECTRODE AND SPACED THEREFROM; CONTACT MEANS FOR CONNECTING EACH CYLINDER TO THE ELECTRODE SURROUNDED THEREBY; THREE PAIRS OF CONDUCTORS LOCATED AT COMMON LEVEL PARALLEL TO THE LEVEL OF THE CYLINDERS AND SPACED AWAY FROM SAID CONTACT MEANS IN A DIRECTION AWAY FROM THE TIPS OF THE ELECTRODES; EACH SAID PAIR OF CONDUCTORS BEING ADAPTED TO BE CONNECTED EXTERIOR THE ELECTRODE CONFIGURATION TO SEPARATE PHASE VOLTAGES AND EACH PAIR HAVING THE CONDUCTORS THEREOF ARRANGED IN CLOSE PROXIMITY FOR FLUX CANCELLATION AND ALL SAID PAIRS EXTENDING FROM EXTERIOR THE ELECTRODE CONFIGURATION THROUGH DIFFERENT SIDES THEREOF TO DIFFERENT POSITIONS INTERIOR THE ELECTRODE CONFIGURATION SUBSTANTIALLY EQUIDISTANT FROM ALL THE ELECTRODES, THE CONDUCTORS OF EACH PAIR BEING SEPARATED AT SAID EQUIDISTANT POSITIONS, ONE SEPARATED CONDUCTOR OF EACH GIVEN PAIR EXTENDING DIRECTLY TO THE CYLINDER ENCLOSING ONE OF THE ELECTRODES DEFINING THE SIDE OF THE CONFIGURATION THROUGH WHICH SAID GIVEN PAIR PASSES AND THE OTHER SEPARATED CONDUCTOR OF THE GIVEN PAIR EXTENDING DIRECTLY TO THE CYLINDER ENCLOSING THE OTHER ELECTRODE DEFINIG THE SIDE OF THE CONFIGURATION THROUGH WHICH SAID GIVEN PAIR PASSES; THE CONDUCTORS EXTENDING TO A COMMON CYLINDER BEING ARRANGED IN CLOSE PROXIMITY FOR FLUX CANCELLATION AND CONNECTED TO EACH OTHER AT THE COMMON CYLINDER. 